1. Field of the Invention
The present invention is useful bonding low-energy plastic surfaces to each other, for example, in construction, automotive applications, plastic fabricating, packaging, structural foam bonding, etc. The adhesive composition described herein is effective in bonding low-energy plastic surfaces to each other which provides an improved low temperature performance containing the following components: (1) a first ethylene-vinyl ester copolymer having from about 4 to about 35 weight percent of a vinyl ester; (2) a second ethylene-vinyl ester copolymer having an excess of 35 weight percent of a vinyl ester; (3) a tackifier selected from the following group (a) a rosin (b) a rosin ester, (c) a terpene resin, (d) a terpene-phenolic resin and (e) a rosin-modified phenolic resin, and (4) a polyethylene wax having a molecular weight of about 600 to about 3000 and a process for bonding low-energy plastic surfaces to each other.
2. Description of the Prior Art
Ordinarily, adhesive bonding of low-energy plastic surfaces to each other requires some form of surface treatment prior to application of an adhesive to obtain high bond strengths between the surfaces so contacted. Low-energy plastic surfaces bonded to each other without prior surface treatment, such as by relatively weak, tacky adhesives, are inadequate for many purposes such as those requiring strengths in a range in excess of several hundreds or thousands of pounds per square inch gauge of bonded area.
For strong bonds involving low-energy plastic surfaces, some form of surface treatment or etching is required prior to application of an adhesive. Surface pretreatment of low-energy plastic surfaces, for example, involves either acid etching with sulfuric, nitric, chromic acids or mixtures thereof, or flame treatment, corona discharge treatment, treatment with plasma jets or low and high energy radiation.
Adhesive compositions which may be used for bonding low-energy plastic surfaces, but requiring surface treatment, include polysulfide-rubber modified epoxies, epoxy-polyamides, nitrile-phenolics and polyesters. These compositions, may additionally, require long hours of post-cure and/or clamping at temperatures substantially higher than room temperature. Often at least two of the components of these adhesive compositions must be premixed prior to application.
Consequently, a need exists for an adhesive composition and much simplier process for bonding low-energy plastic surfaces to each other for low temperature performance. In accordance with the present invention a novel hot melt adhesive composition is provided which requires minimal heating of the surfaces to be bonded together and maximum bond strength is obtained in a matter of minutes or a few hours without resort to elaborate post-curing procedures. Further, the adhesive composition of the present invention can be applied in its melt form to low-energy plastic surfaces in such a manner to provide rapid assembly of components and immediate handling of the assembled parts. Another advantage of the present invention is that the bonds can deliver improved tensile lap shear strengths at low temperature.
Applicant is unaware of any prior art relevant to the invention defined and claimed herein.